Evolution, Old & New Part 23

The reader has now before him a fair sample of "the well-known doctrine of inherited habit as advanced by Lamarck."[287] In what way, let me ask in pa.s.sing, does "the case of neuter insects" prove "demonstrative"

against it, unless it is held equally demonstrative against Mr. Darwin's own position? Lamarck continues:--

"The character of any habitable quarter of the globe is _qua_ man constant: the constancy of type in species is therefore also _qua_ man persistent. But this is an illusion. We establish, therefore, the three following propositions:--

"1. That every considerable and sustained change in the surroundings of any animal involves a real change in its needs.

"2. That such change of needs involves the necessity of changed action in order to satisfy these needs, and, in consequence, of new habits.[288]

"3. It follows that such and such parts, formerly less used, are now more frequently employed, and in consequence become more highly developed; new parts also become insensibly evolved in the creature by its own efforts from within.

"From the foregoing these two general laws may be deduced:--

"_Firstly. That in every animal which has not pa.s.sed its limit of development, the more frequent and sustained employment of any organ develops and aggrandizes it, giving it a power proportionate to the duration of its employment, while the same organ in default of constant use becomes insensibly weakened and deteriorated, decreasing imperceptibly in power until it finally disappears._[289]

"_Secondly. That these gains or losses of organic development, due to use or disuse, are transmitted to offspring, provided they have been common to both s.e.xes, or to the animals from which the offspring have descended._"[290]

Lamarck now sets himself to establish the fact that animals have developed modifications which have been transmitted to their offspring.

"Naturalists," he says, "have believed that the possession of certain organs has led to their employment. This is not so: it is need and use which have developed the organs, and even called them into existence."

[I have already sufficiently insisted that it is impossible to dispense with either of these two views. Demand and Supply have gone hand in hand, each reacting upon the other.] "Otherwise a special act of creation would be necessary for every different combination of conditions; and it would be also necessary that the conditions should remain always constant.

"If this were really so we should have no racehorses like those of England, nor drayhorses so heavy in build and so unlike the racehorse; for there are no such breeds in a wild state. For the same reason, we should have no turnspit dogs with crooked legs, no greyhounds nor water-spaniels; we should have no tailless breed of fowls nor fantail pigeons, &c. Nor should we be able to cultivate wild plants in our gardens, for any length of time we please, without fear of their changing.

"'Habit,' says the proverb, 'is a second nature'; what possible meaning can this proverb have, if descent with modification is unfounded?[291]

"As regards the circ.u.mstances which give rise to variation, the princ.i.p.al are climatic changes, different temperatures of any of a creature's environments, differences of abode, of habit, of the most frequent actions; and lastly, of the means of obtaining food, self-defence, reproduction, &c., &c."[292]

Here we have absolute agreement with Dr. Erasmus Darwin,[293] except that there seems a tendency in this pa.s.sage to a.s.sign more effect to the direct action of conditions than is common with Lamarck. He seems to be mixing Buffon and Dr. Darwin.

"In consequence of change in any of these respects, the faculties of an animal become extended and enlarged by use: they become diversified through the long continuance of the new habits, until little by little their whole structure and nature, as well as the organs originally affected, partic.i.p.ate in the effects of all these influences, and are modified to an extent which is capable of transmission to offspring."[294]

This sentence alone would be sufficient to show that Lamarck was as much alive as Buffon and Dr. Darwin were before him, to the fact that one of the most important conditions of an animal's life, is the relation in which it stands to the other inhabitants of the same neighbourhood--from which the survival of the fittest follows as a self-evident proposition.

Nothing, therefore, can be more unfounded than the attempt, so frequently made by writers who have not read Lamarck, or who think others may be trusted not to do so, to represent him as maintaining something perfectly different from what is maintained by modern writers on evolution. The difference, in so far as there is any difference, is one of detail only. Lamarck would not have hesitated to admit, that, if animals are modified in a direction which is favourable to them, they will have a better chance of surviving and transmitting their favourable modifications. In like manner, our modern evolutionists should allow that animals are modified not because they subsequently survive, but because they have done this or that which has led to their modification, and hence to their surviving.

Having established that animals and plants are capable of being materially changed in the course of a few generations, Lamarck proceeds to show that their modification is due to changed distribution of the use and disuse of their organs at any given time.

"_The disuse of an organ_," he writes, "_if it becomes constant in consequence of new habits, gradually reduces the organ, and leads finally to its disappearance_."[295]

"Thus whales have lost their teeth, though teeth are still found in the embryo. So, again, M. Geoffroy has discovered in birds the groove where teeth were formerly placed. The ant-eater, which belongs to a genus that has long relinquished the habit of masticating its food, is as toothless as the whale."[296]

Then are adduced further examples of rudimentary organs, which will be given in another place, and need not be repeated here. Speaking of the fact, however, that serpents have no legs, though they are higher in the scale of life than the batrachians, Lamarck attributes this "to the continued habit of trying to squeeze through very narrow places, where four feet would be in the way, and would be very little good to them, inasmuch as more than four would be wanted in order to turn bodies that were already so much elongated."[297]

If it be asked why, on Lamarck's theory, if serpents wanted more legs they could not have made them, the answer is that the attempt to do this would be to unsettle a question which had been already so long settled, that it would be impossible to reopen it. The animal must adapt itself to four legs, or must get rid of all or some of them if it does not like them; but it has stood so long committed to the theory that if there are to be legs at all, there are to be not more than four, that it is impossible for it now to see this matter in any other light.

The experiments of M. Brown Sequard on guinea pigs, quoted by Mr.

Darwin,[298] suggest that the form of the serpent may be due to its having lost its legs by successive accidents in squeezing through narrow places, and that the wounds having been followed by disease, the creature may have bitten the limbs off, in which case the loss might have been very readily transmitted to offspring; the animal would accordingly take to a sinuous mode of progression that would doubtless in time elongate the body still further. M. Brown Sequard "carefully recorded" thirteen cases, and saw even a greater number, in which the loss of toes by guinea pigs which had gnawed their own toes off, was immediately transmitted to offspring. Accidents followed by disease seem to have been somewhat overlooked as a possible means of modification.

The missing forefinger to the hand of the potto[299] would appear at first sight to have been lost by some such mishap. Returning to Lamarck, we find him saying:--

"Even in the lifetime of a single individual we can see organic changes in consequence of changed habits. Thus M. Tenon has constantly found the intestinal ca.n.a.l of drunkards to be greatly shorter than that of people who do not drink. This is due to the fact that habitual drunkards eat but little solid food, so that the stomach and intestines are more rarely distended. The same applies to people who lead studious and sedentary lives. The stomachs of such persons and of drunkards have little power, and a small quant.i.ty will fill them, while those of men who take plenty of exercise remain in full vigour and are even increased."[300]

It becomes now necessary to establish the converse proposition, namely that:--

"_The frequent use of an organ increases its power; it even develops the organ itself, and makes it acquire dimensions and powers which it is not found to have in animals which make no use of such an organ._

"In support of this we see that the bird whose needs lead it to the water, in which to find its prey, extends the toes of its feet when it wants to strike the water, and move itself upon the surface. The skin at the base of the toes of such a bird contracts the habit of extending itself from continual practice. To this cause, in the course of time, must be attributed the wide membrane which unites the toes of ducks, geese, &c. The same efforts to swim, that is to say, to push the water for the purpose of moving itself forward, has extended the membrane between the toes of frogs, turtles, the otter, and the beaver."[301]

[This is taken, I believe, from Dr. Darwin or Buffon, but I have lost the pa.s.sage, if, indeed, I ever found it. It had been met by Paley some years earlier (1802) in the following:--

"There is nothing in the action of swimming as carried on by a bird upon the surface of the water that should generate a membrane between the toes. As to that membrane it is an action of constant resistance.... The web feet of amphibious quadrupeds, seals, otters, &c., fall under the same observation."[302]]

"On the other hand those birds whose habits lead them to perch on trees, and which have sprung from parents that have long contracted this habit, have their toes shaped in a perfectly different manner. Their claws become lengthened, sharpened, and curved, so as to enable the creature to lay hold of the boughs on which it so often rests. The sh.o.r.e bird again, which does not like to swim, is nevertheless continually obliged to enter the water when searching after its prey. Not liking to plunge its body in the water, it makes every endeavour to extend and lengthen its lower limbs. In the course of long time these birds have come to be elevated, as it were, on stilts, and have got long legs bare of feathers as far as their thighs, and often still higher. The same bird is continually trying to extend its neck in order to fish without wetting its body, and in the course of time its neck has become modified accordingly.[303]

"Swans, indeed, and geese have short legs and very long necks, but this is because they plunge their heads as low in the water as they can in their search for aquatic larvae and other animalcules, but make no effort to lengthen their legs."[304]

This too is taken from some pa.s.sage which I have either never seen or have lost sight of. Paley never gives a reference to an opponent, though he frequently does so when quoting an author on his own side, but I can hardly doubt that he had in his mind the pa.s.sage from which Lamarck in 1809 derived the foregoing, when in 1802 he wrote -- 5 of chapter xv. and the latter half of chapter xxiii. of his 'Natural Theology.'

"The tongues of the ant-eater and the woodp.e.c.k.e.r," continues Lamarck, "have become elongated from similar causes. Humming birds catch hold of things with their tongues; serpents and lizards use their tongues to touch and reconnoitre objects in front of them, hence their tongues have come to be forked.

"Need--always occasioned by the circ.u.mstances in which an animal is placed, and followed by sustained efforts at gratification--can not only modify an organ, that is to say, augment or reduce it, but can change its position when the case requires its removal.[305]

"Ocean fishes have occasion to see what is on either side of them, and have their eyes accordingly placed on either side their head. Some fishes, however, have their abode near coasts on submarine banks and inclinations, and are thus forced to flatten themselves as much as possible in order to get as near as they can to the sh.o.r.e. In this situation they receive more light from above than from below, and find it necessary to pay attention to whatever happens to be above them; this need has involved the displacement of their eyes, which now take the remarkable position which we observe in the case of soles, turbots, plaice, &c. The transfer of position is not even yet complete in the case of these fishes, and the eyes are not, therefore, symmetrically placed; but they are so with the skate, whose head and whole body are equally disposed on either side a longitudinal section. Hence the eyes of this fish are placed symmetrically upon the uppermost side.[306]

"The eyes of serpents are placed on the sides and upper portions of the head, so that they can easily see what is on one side of them or above them; but they can only see very little in front of them, and supplement this deficiency of power with their tongue, which is very long and supple, and is in many kinds so divided that it can touch more than one object at a time; the habit of reconnoitring objects in front of them with their tongues has even led to their being able to pa.s.s it through the end of their nostrils without being obliged to open their jaws.[307]

"Herbivorous mammals, such as the elephant, rhinoceros, ox, buffalo, horse, &c., owe their great size to their habit of daily distending themselves with food and taking comparatively little exercise. They employ their feet for standing, walking, or running, but not for climbing trees. Hence the thick horn which covers their toes. These toes have become useless to them, and are now in many cases rudimentary only.

Some pachyderms have five toes covered with horn; some four, some three. The ruminants, which appear to be the earliest mammals that confined themselves to a life upon the ground, have but two hooves, while the horse has only one.[308]

"Some herbivorous animals, especially among the ruminants, have been incessantly preyed upon by carnivorous animals, against which their only refuge is in flight. Necessity has therefore developed the light and active limbs of antelopes, gazelles, &c. Ruminants, only using their jaws to graze with, have but little power in them, and therefore generally fight with their heads. The males fight frequently with one another, and their desires prompt an access of fluids to the parts of their heads with which they fight; thus the horns and bosses have arisen with which the heads of most of these animals are armed.[309] The giraffe owes its long neck to its continued habit of browsing upon trees, whence also the great length of its fore legs as compared with its hinder ones. Carnivorous animals, in like manner, have had their organs modified in correlation with their desires and habits. Some climb, some scratch in order to burrow in the earth, some tear their prey; they therefore have need of toes, and we find their toes separated and armed with claws. Some of them are great hunters, and also plunge their claws deeply into the bodies of their victims, trying to tear out the part on which they have seized; this habit has developed a size and curvature of claw which would impede them greatly in travelling over stony ground; they have therefore been obliged to make efforts to draw back their too projecting claws, and so, little by little, has arisen the peculiar sheath into which cats, tigers, lions, &c., withdraw their claws when they no longer wish to use them.[310]

"We see then that the long-sustained and habitual exercise of any part of a living organism, in consequence of the necessities engendered by its environment, develops such part, and gives it a form which it would never have attained if the exercise had not become an habitual action.

All known animals furnish us with examples of this.[311] If anyone maintains that the especially powerful development of any organ has had nothing to do with its habitual use--that use has added nothing, and disuse detracted nothing from its efficiency, but that the organ has always been as we now see it from the creation of the particular species onwards--I would ask why cannot our domesticated ducks fly like wild ducks? I would also quote a mult.i.tude of examples of the effects of use and disuse upon our own organs, effects which, if the use and disuse were constant for many generations, would become much more marked.

"A great number of facts show, as will be more fully insisted on, that when its will prompts an animal to this or that action, the organs which are to execute it receive an excess of nervous fluid, and this is the determinant cause of the movements necessary for the required action.

Modifications acquired in this way eventually become permanent in the breed that has acquired them, and are transmitted to offspring, without the offspring's having itself gone through the processes of acquisition which were necessary in the case of the ancestor.[312] Frequent crosses, however, with unmodified individuals, destroy the effect produced. It is only owing to the isolation of the races of man through geographical and other causes, that man himself presents so many varieties, each with a distinctive character.

"A review of all existing cla.s.ses, orders, genera, and species would show that their structure, organs, and faculties, are in all cases solely attributable to the surroundings to which each creature has been subjected by nature, and to the habits which individuals have been compelled to contract; and that they are not at all the result of a form originally bestowed, which has imposed certain habits upon the creature.[313]

"It is unnecessary to multiply instances; the fact is simply this, that all animals have certain habits, and that their organization is always in perfect harmony with these habits.[314] The conclusion hitherto accepted is that the Author of Nature, when he created animals, foresaw all the possible circ.u.mstances in which they would be placed, and gave an unchanging organism to each creature, in accordance with its future destiny. The conclusion, on the other hand, here maintained is that nature has evolved all existing forms of life successively, beginning with the simplest organisms and gradually proceeding to those which are more complete. Forms of life have spread themselves throughout all the habitable parts of the earth, and each species has received its habits and corresponding modification of organs, from the influence of the surroundings in which it found itself placed.[315]

"The first conclusion supposes an unvarying organism and unvarying conditions. The second, which is my theory (_la mienne propre_), supposes that each animal is capable of modifications which in the course of generations amount to a wide divergence of type.

"If a single animal can be shown to have varied considerably under domestication, the first conclusion is proved to be inadmissible, and the second to be in conformity with the laws of nature."

This is a milder version of Buffon's conclusion (see _ante_, pp. 90, 91). It is a little grating to read the words "la mienne propre,"

and to recall no mention of Buffon in the 'Philosophie Zoologique.'

"Animal forms then are the result of conditions of life and of the habits engendered thereby. With new forms new faculties are developed, and thus nature has little by little evolved the existing differentiations of animal and vegetable life."[316]